This invention relates to a superconduction storage apparatus of electrical power with an improved operating efficiency.
FIG. 1 shows an example of a conventional superconduction power storage apparatus. In FIG. 1, the reference numeral 1 designates a superconduction coil for storage and release of electrical energy; reference numeral 2 designates a separately excited thyristor conversion unit having a.c. terminals and d.c. terminals; reference numeral 3 designates an a.c. power source. The thyristor conversion unit 2 has its d.c. terminals 4 connected directly to the superconduction coil 1 and has its a.c. terminals 5 connected to the a.c. power source 3 by way of a transformer 6.
The operation of the conventional storage apparatus shown in FIG. 1 is as follows. The a.c. power from the a.c. power source 3 is converted into d.c. power by the conversion unit 2 and supplied to the superconduction coil 1 for storage, the thyristor conversion unit 2 then operating as a forward conversion apparatus.
The d.c. electrical energy thus stored in the superconduction coil 1 is released into the a.c. power source as a.c. power by the reverse conversion operation of the thyristor conversion unit 2.
Such storage and release of the electrical energy may be controlled by adjusting the d.c. terminal voltage of the thyristor conversion unit 2 by the phase control of the thyristor conversion unit 2, thereby changing the d.c. voltage applied to the superconduction coil 1.
As the d.c. voltage of the thyristor conversion unit 2 is applied to the coil 1, a ripple current flows due to voltage ripple contained in such a d.c. voltage, thus causing an eddy current loss due to such a ripple current. This eddy current loss may raise the temperature of the superconduction coil 1 and may eventually give rise to destruction of the superconduction state of the coil 1. Hence, the coil 1 must be cooled by a cooling apparatus which is not shown.
In the case of using a liquid helium at 4.degree. K. or thereabouts as a cooling medium for the superconduction coil 1, the removal of heat quantity of 1 joule requires an energy of about 300 times that value.
Hence, in the superconduction power storage apparatus, the magnitude of the d.c. voltage ripple applied to the superconduction coil 1 affects the operating efficiency of the apparatus.
In this consideration, the superconduction power storage apparatus of the prior art has such a drawback that, since the voltage applied to the superconduction coil 1 is adjusted in its entirety by the phase control of the thyristor control unit 2, the lesser the absolute value of the electrical voltage applied to the coil 1, the larger is the voltage ripple, thus causing an increased eddy current loss in the coil 1 and an increased cooling load.